US 4,487,784 AGranted

Limestone-gypsum flue gas desulfurization process

AssigneeBabcock-Hitachi Kabushiki Kaisha

InventorsHiroshi Kuroda, Tsukasa Nishimura, Taiki Hashimoto, Masakatsu Nishimura, Osamu Kanda, Shigeru Nozawa

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Abstract

A flue gas desulfurization process capable of producing a high purity gypsum and also making equipment employed as minimum as possible is provided, which process comprises the steps of cooling and dedusting flue gas containing SO.sub.x ; contacting the cooled gas with a slurry containing limestone to remove SO.sub.x by absorption and also form CaSO.sub.3 ; controlling the pH of the resulting slurry and then blowing air therein to form gypsum; and separating gypsum from the resulting slurry. As a modification of the above process, the slurry of the above second absorption step is further fed to the above first cooling step where unreacted limestone and SO.sub.x are reacted to form CaSO.sub.3.

Claims31

Dependent claims

A limestone-gypsum flue gas desulfurization process comprising:

a cooling step of cooling and dedusting flue gas containing sulfur oxides (SO.sub.x) and producing an effluent;
an absorption step of contacting the flue gas cooled in said cooling step with a limestone (lime) slurry to absorb and remove the SO.sub.x contained in the gas thereby forming CaSO.sub.3 and CA(HSO.sub.3).sub.2 and producing cleaned gas;
controlling the pH of the resulting slurry containing CaSO.sub.3 L and Ca(HSO.sub.3).sub.2 formed in said absorption step to less than 5;
an oxidation step of contacting the resulting slurry from said pH-adjusting step with air to oxidize it and thereby form gypsum wherein the air is supplied in an amount of 1.5 to 3 times the theoretical amount of air;
a liquid-separation step of concentrating the resulting slurry containing gypsum from said oxidation step to produce clarified water and a gypsum slurry;
a centrifugal separation step of separating gypsum from the concentrated gypsum slurry to produce gypsum and a filtrate containing fine particles of gypsum;
adding an ion exchange resin to the separated clarified water to absorb dithionic ions contained in the clarified water followed by desorbing at pH 10;
and
treating the desorbed ions at pH 1.5 or less and heating to at least 60.degree. C. to decompose the dithionic ions.

6 more elements

A limestone-gypsum flue gas desulfurization process comprising:

a cooling step of cooling and dedusting flue gas containing sulfur oxides (SO.sub.x) and producing an effluent;
an absorption step of contacting the flue gas cooled in said cooling step with a limestone (lime) slurry to absorb and remove the SO.sub.x contained in the gas thereby forming CaSO.sub.3 and CA(HSO.sub.3).sub.2 and producing cleaned gas;
controlling the pH of the resulting slurry containing CaSO.sub.3 and Ca(HSO.sub.3).sub.2 formed in said absorption step to less than 5;
an oxidation step of contacting the resulting slurry from said pH-adjusting step with air to oxidize it and thereby form gypsum wherein the air is supplied in an amount of 1.5 to 3 times the theoretical amount of air;
a liquid-separation step of concentrating the resulting slurry containing gypsum from said oxidation step to produce a concentrated gypsum slurry and clarified water;
a centrifugal separation step of separating gypsum from the concentrated gypsum slurry to produce gypsum and a filtrate containing fine particles of gypsum;
treating the clarified water separated from the gypsum slurry by adjusting the pH to 1.5 or less and heating to at least 60.degree. C. to decompose dithionic ions.

4 more elements

A limestone-gypsum flue gas desulfurization process which comprises:

a cooling and absorption step of contacting a high temperature SO.sub.x -containing gas with a low temperature limestone (lime) slurry fed from the second step described below, to cool and dedust the gas and to cause the slurry to absorb SO.sub.x in the gas;
a second absorption step of contacting the gas cooled in the cooling step with a limestone slurry to cause the slurry to absorb SO.sub.x -contained in the gas to thereby remove SO.sub.x from the gas and produce cleaned gas;
controlling the pH of the slurry leaving the cooling step to less than 5;
an oxidation step of contacting the slurry led from the pH-adjusting step with air to oxidize the slurry and form gypsum, wherein the air is supplied in an amount 1.5 to 3 times the theoretical amount of air;
a solid-liquid separation step of concentrating the slurry containing gypsum from the oxidation step to produce a concentrated gypsum slurry and clarified water;
a centrifugal separation step of separating gypsum from the concentrated gypsum slurry to produce gypsum and filtrate containing small particles of gypsum;
a step wherein the filtrate is supplied to the slurry in the absorption step so that the gypsum concentration in the absorption slurry is at least 5% by weight;
treating the clarified water separated from the gypsum slurry by adjusting the pH to 1.5 or less and heating to at least 60.degree. C. to decompose dithionic ions.

5 more elements

Dependencies are inferred from the claim text.